RU2490134C2 - Linear polyethylene with high melt yield-to-film yield ratio and films made thereof by coextrusion - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to packing films and method of their production by blow extrusion. Said film comprises, at least two outer layers and at least one inner layer arranged there between. Outer layers comprises at least one linear ethylene copolymer and alpha-olefin with melt yield ratio (I₂₁/I₂) over 20, density varying from 0.910 to 0.945 g/cm³, distribution of molecular weights (Mw/Mn) from 2.0 to 5.0 and composition distribution factor under 40%. Note here that linear copolymer of ethylene and alpha-olefin incorporate component soluble in xylene at 60°C or lower in amount of at least 5 wt %. Film inner layer comprises at least one polyethylene with common density of at least 0.910 g/cm³.

EFFECT: better optical and mechanical properties and manufacturability.

15 cl, 7 tbl, 2 ex

Description

FIELD OF THE INVENTION

The present invention relates to linear copolymers of ethylene and alpha-olefin as film components having a predetermined density and melt flow ratio (OTP), as well as to films obtained by co-extrusion, specifically obtained by co-extrusion blown processes using linear ethylene and alpha olefin. Co-extruded films can be used in packaging. Films have an improved ratio of optical and mechanical properties, and are also more suitable for processing.

BACKGROUND OF THE INVENTION

Film manufacturers have to maintain a balance between A) processability, which determines the maximum achievable yield per film extrusion device in order to reduce production costs, B) mechanical strength, for example, impact strength, in order to obtain more durable films of this thickness and reduce total polymer consumption to provide these characteristics, and B) optical properties such as turbidity.

Films obtained from linear low-density polyethylene using traditional Ziegler-Natta catalysts (cnlnp) are known to have favorable physical properties, for example, high tensile strength. Films obtained from linear low-density polyethylene using metallocene catalysts (MLPNP) have improved tensile and puncture strengths, as well as improved impact resistance. Thus, the film industry continues to search for polyethylene films having advantageous properties similar or improved compared to films made from cnLDPL, while retaining the advantages of films made from mLLP.

Although there are previously described methods and polymers in the art that utilize some linear copolymers of ethylene and alpha-olefin, none of them describe multilayer films having an impact strength determined by a falling point load (ASTM D1709) in excess of 10 g / μm and a turbidity (ASTM D1003, method B) of less than 10%. Single-layer blown films and having improved strength when tested with a falling pointed load (compared to films made from MLPDs) are described in US Pat. No. 6,956,088. The present invention provides multilayer blown films having an improved combination of properties, specifically improved impact strength compared to currently used LDL, with comparable or higher transparency.

SUMMARY OF THE INVENTION

In one preferred embodiment, a blown film is described comprising at least two outer layers and at least one inner layer located between the outer layers, the film having an impact strength determined by a falling pointed load (ASTM D1709) in excess of 10 g / μm and a turbidity (ASTM D1003, method B) of less than 10%, a tensile strength in the longitudinal direction of more than 45 MPa, and a tensile strength in the transverse direction of more than 35 MPa.

Also described is a blown film comprising at least two outer layers and at least one inner layer located between the outer layers, the film having an impact strength determined by a falling pointed load (ASTM D1709) greater than 10 g / μm, and a turbidity (ASTM D1003, method B) of less than 10%, in which the inner layer includes at least one polyethylene, the total density of which is at least 0.910 g / cm ³ and the outer layers include at least one linear copolymer ep ethylene and alpha-olefin, the ratio of I ₂₁ \ I ₂ which is more than 20, the density of the outer layers is from 0.910 to 0.945 g / cm, Mw / Mn is from 2.0 to 5.0, and at least 5 % of the mass. which is soluble in xylene at 60 ° C or less, and the soluble part has the following properties:

- Mw (determined by gel permeation chromatography) is 150,000 g / mol or more;

- includes at least 5% mole. C ₃ -C ₂₀ comonomer as determined by ¹³ C NMR;

- the value of r ₁ r ₂ is 1.0 or less;

- the number of "butyl" groups per 1000 carbon atoms is 15 or more.

In addition, a method for producing a film is described, comprising coextruding through a round melt head a composition of at least one inner layer having two faces and a composition of at least one outer layer comprising one or more linear ethylene and alpha copolymers α-olefin, each of the outer layers being located next to each side of the inner layer, followed by stretching the molten polymers in the form of a tube by extrusion blown layered melts with the formation of a bubble using air fed through the die, the film obtained by extrusion of one or more linear copolymers of ethylene and alpha-olefin through a die to form a film blown at a tensile rate of 2 s ^-1 or more, the processing time is 2 s or less, a degree of inflation of 2.5 or less, a freezing line height of 1.0 m or less, and a head capacity of 2.0 kg / h / cm of head circumference or more.

The various definitions and numerical ranges described herein can be combined with other definitions and numerical ranges to describe preferred options for the film (s) or compositions that make up the film (s); in addition, any upper bound on the numerical range of an element can be combined with any lower bound on the values of the same element in order to describe preferred options. In this regard, it is determined that the expression “in the range from X to Y” includes the values “X” and “Y” in this range.

Detailed Description of the Invention

The present disclosure describes blown multilayer films having an outer layer (s) comprising at least one linear copolymer of ethylene and alpha-olefin having exceptional impact strength and transparency. The inner layer (s) of such films includes “polyethylenes” (linear copolymers of ethylene and alpha-olefin, HDPE, LDL, LDPE, and a mixture of the above), and consists essentially of polyethylene in a particular preferred embodiment. A “linear copolymer of ethylene and alpha-olefin” is a polyolefin that combines the positive qualities of the mLDPE known in the art from the formation of films with the positive qualities of the cnLDPs known to the art of the film forming, and such a linear copolymer is described more specifically below. Films can be characterized using a number of parameters, but in one preferred embodiment, a blown film is described that includes at least two outer layers and at least one inner layer located between the outer layers, the outer layer (s) includes at least one linear copolymer of ethylene and alpha-olefin having a ratio of I ₂₁ \ I ₂ (21.6 / 2.16 kg, 190 ° C) of more than 20, and a density of from 0.910 to 0.945 g / cm ³ . The characteristics of this film (s), individually or in combination, are impact strength determined using a falling pointed load (ASTM D1709) of more than 10 g / μm and turbidity (ASTM D1003, method B) of less than 10%. Films can be further described using the various properties below.

As used herein, the term “layer” refers to one or more of the same or different compositions attached to each other in the form of thin plates or films in any suitable manner, for example, by the inherent ability of such materials to adhere to each other, or by forcing the compositions to be glued together for example, by exposure to heat, radiation, chemicals, or other suitable method. The expression “layer” is not limited to clearly distinguishable separate compositions in contact with each other in such a way that there is a distinct border between them. However, preferably, the composition used to produce one film layer will be different (that is, the mass contents of the components, the properties of each component and / or the types of components may differ) from the composition used to produce the adjacent layer, if present. The expression "film" includes the final product containing continuous compositions over its entire thickness. The expression “films” described herein includes at least two, three or more layers.

Suitable film (“film”) structures include, for example, “ABA” structures, wherein a film having an ABA or A'BA structure (A differs from A ′) has three layers, with layer B being inner and outer layers “ A ”are on one of the sides of“ B ”or on both sides. Each of the layers “A” or “B” of the film may be the same or different. Non-limiting examples of other structures of the present invention include AB, ABAB, ABA, AAB, AA'B, AABAA, BABBA, ABAA, ABBAB, ABBABB, ABBA, ABBAB, ABA'BA ”B, AABBBA and other options, including from 2 or 3 to 5 or 6 or 7 or 8 or more layers. In a particular preferred embodiment, the films are of type AB and ABA, where “A” includes a linear copolymer of ethylene and alpha-olefin, and layer “B” includes one or more types of “polyethylene”. In certain preferred embodiments, the films and / or any layer of films described herein does not contain propylene-based polymers. By the term "propylene-based polymers" is meant polymers comprising at least 50% of the mass. propylene units.

As used herein, the term “linear low density polyethylene” (“LDL”) is understood to mean a polyethylene homopolymer or copolymer prepared using a transition metal catalyst having a density of 0.910 to 0.935 g / cm. The polymers called linear polyethylenes above can be prepared using various catalytic systems. The prefix "cn", for example, in the expression "cnLDPE", is used in the present description and claims to describe the fact that the traditional Ziegler-Natta catalyst system was used in the preparation of the polymer, typically using a titanium compound as a transition metal, and aluminum alkyl as a cocatalyst. It is generally believed that such catalysts have several types of active sites providing different catalytic activity. The expression "MLPNP" means that the transition metal component used was a catalyst with one kind of active site, which usually refers to a transition metal component such as a metallocene or a metal imide / amine compound activated by well known activation methods such components, for example, using alumoxane or non-coordinating anion. In the interest of convenience, polyethylene obtained using catalysts with one type of active site other than metallocene is also designated using the prefix "m". Different catalysts affect the molecular weight distribution, composition distribution, the arrangement of the units and groups located at the ends of the chain, which, together with the analysis of the catalyst residue, allows persons skilled in the art to easily distinguish between types of mLCL and cnLDP. Linear polyethylene of the “cn” type, as a rule, has a higher heterogeneity with respect to the distribution of molecular weight and distribution of composition, compared with linear polyethylene of the “m” class, which is determined by the nature of the catalyst containing several types of active sites. Heterogeneity can be determined using fractionation techniques suitable for a given density, for example, by measuring the molecular weight distribution using GPC, studying the distribution of the composition by elution fractionation with increasing temperature (EFT) or crystallization fractionation. In the present description and claims, linear “polyethylene” type polyethylenes refer to polyethylenes that can be analyzed by elution fractionation, for which the T ₇₅ -T ₂₅ value determined as described in the present description is at least 20 ° C. optionally, they also have a low T ₂₅ , typically less than 70 ° C, which indicates the presence of a significant amount of an easily eluting fraction of a polymer based on a higher low molecular weight comonomer. In the case of low density polymers, other fractionation techniques can be used to recognize linear polyethylene of types “cn” and “m”. The above LDL-C polymers are well known in the art and can be prepared by conventional polymerization methods.

"High density polyethylene" ("PVP") is a homopolymer or copolymer of polyethylene, the density of which is more than 0.945 g / cm or more, and PVP is well known in the art. Examples of suitable PVPs include ExxonMobil ™ high density polyethylene and Paxon ™ high density polyethylene (ExxonMobil Chemical Co.).

As used herein, the expression “high pressure polyethylene” (“LDPE”) is understood to mean a free radical-initiated polymerization product comprising at least 85% mole. units derived from ethylene. The resulting polymer is usually described as having a non-linear structure and heterogeneous branching. It is believed that heterogeneous branches in LDPE are the result of the introduction of branches with short and long chains of various sizes and structures. LDPE polymerization is initiated using free radicals, which leads to heterogeneous introduction of branches of various lengths and structures into the main chain by the so-called “back-biting” mechanism. Such polymers have high nonlinearity. ¹³ With the NMR, the LDPE spectrum indicates a statistically probable distribution of shorter chains, and this spectrum differs from the linear polyethylene spectra, for which the NMR peaks corresponding to the short chains are the result of short chain branching formed upon the introduction of the comonomer. LDPE includes (A) low density polyethylene (HDPE), which in the present description is defined as containing less than 7.5% mole. units derived from comonomers containing polar moieties, for example carbonyl groups, including ethylenically unsaturated esters, for example vinyl acetate, ethylene methyl acrylate, ethylene methacrylic acid or ethylene acrylic acid, and (B) heterogeneously branched ethylene vinyl acetate containing more than 7.5% mole . such a comonomer, including polar groups. If LDPE is used, its density may be more than 0.900 g / cm, preferably it is from 0.920 to 0.940 g / cm. The molecular weight distribution of the Mw / Mn LDPE determined by GPC can be from 5 to 40.

Used in the present description, the expression "linear copolymers of ethylene and alpha-olefin" is described in detail in USSN 12/130135, filed May 13, 2008, incorporated herein by reference. Such copolymers contain individual chains having similar carbon chain lengths (narrow PMM), but they have a wide distribution of comonomer units in chains (low distribution width index of the composition (ISRS)), i.e., some chains contain almost no units that are derivatives of comonomer, and other chains contain a large number of such links. Various parameters used to describe linear copolymers of ethylene and alpha-olefin are defined in methods based on the present description, or known in the art.

In certain preferred embodiments, the linear ethylene-alpha-olefin copolymer comprises at least 75% mole. or 80% mole. or 90% mole. or 95% mole. ethylene units. In certain preferred embodiments, linear ethylene-alpha-olefin copolymers are linear low density polyethylene resins obtained by polymerization of ethylene and, optionally, alpha-olefin comonomer containing from 3 to 20 carbon atoms, 1-hexene, in a particularly preferred embodiment, using a catalyst and an activator, further described below. Linear copolymers of ethylene and alpha olefin may contain up to 25% mole. alpha-olefin comonomer introduced into the copolymer, in some preferred embodiments, from 0.5 to 4 or 15% mole.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have a melt index (I ₂ , 2.16 kg, 190 ° C.) of 0.1 to 10 dg / min, 0.2 to 5 dg / min in another in a preferred embodiment, and from 0.4 to 4 dg / min in yet another preferred embodiment, in a particular preferred embodiment, from 0.1 to 1.0 dg / min.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have a melt index at elevated shear stress (I ₂₁ , 21.6 kg, 190 ° C.) of 51 to 60 dg / min, in another preferred embodiment 10 to 40 dg / min, in a particular preferred embodiment, from 15 to 35 dg / min.

In certain preferred embodiments, linear copolymers of ethylene and alpha-olefin with a relatively high melt flow ratio ("OTP" or I ₂₁ / I ₂ ) have an I ₂₁ \ I ₂ of 20 or 25 to 30 or 35 or 40 or 50 or 60 or 70 or 80. In other preferred embodiments, linear ethylene-alpha olefin copolymers have an I ₂₁ / I ₂ ratio of greater than 20 or 25 or 30.

In certain preferred embodiments, the density of linear copolymers of ethylene and alpha-olefin is from 0.910 to 0.945 g / cm ³ , from 0.920 to 0.940 g / cm in another preferred embodiment, from 0.921 to 0.935 g / cm in another preferred embodiment, and from 0.922 to 0.930 g / cm ³ in yet another embodiment.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have an Mw / Mn of 2.5 to 5.0, in another preferred embodiment of 2.5 to 4.5, from 2.8 to 4.5, still one of the preferred options, from 2.8 to 4.0 in another of the preferred options, and from 2.8 to 5.0 in another preferred embodiment. In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have an Mz / Mw of 2.0 to 3.0 or 4.0.

In certain preferred embodiments, linear copolymers of ethylene and alpha-olefin include a portion soluble in xylene at 60 ° C or less, comprising at least 5 or 8 or 10% of the mass. (alternatively, from 5 to 8 or 10 or 15 or 20 wt.%), and the soluble part has (in accordance with the fractionation of chemical compositions described below) the following properties:

- Mw (GPC) is 150,000 g / mol or more, 200,000 g / mol or more in another preferred embodiment, 250,000 g / mol or more in another preferred embodiment, in yet another embodiment, the upper limit of Mw is 600,000 g / mol or 1,000,000 g / mol,

- ISRS is more than 90 or 95,

- Mw / Mn is from 3 or 4 or 5 to 10 or 15 or 20 in certain preferred embodiments, is more than 4 or 5 or 8 or 10 in other preferred embodiments, and Mw / Mn is from 1.0 or 1.2 up to 2.5 or 3.0,

- contains at least 5 or 6 or 7% mole. units derived from comonomer, in certain preferred embodiments, and from 4 or 5% mole. up to 10 or 12 or 15% mole. in other preferred embodiments, wherein the comonomer is a derivative of C ₃ -C ₂₀ olefins in one embodiment, is a derivative of C ₄ -C ₁₂ alpha olefins in another embodiment, and is a derivative of 1-hexene, 1-octene and / or 1 -butene in a specific preferred embodiment, and the molar content (% mol.) determined using ¹³ C NMR,

- the value of r ₁ r ₂ is 1.0 or 0.9 or 0.8 or 0.7 or less in certain preferred embodiments, is from 0.5 or 0.6 to 1.0 or 2.0 in other preferred embodiments , and

- the content of "butyl" groups per 100 carbon atoms is more than 15 or 20 or 25 or 30 or 35 or 40 in certain preferred embodiments, and from 5 or 10 or 15 to 20 or 25 or 30 or 40 or 50 in others preferred options.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have a broad (i.e., less than 40%) composition distribution, measured based on the composition distribution width index (ISRS). For example, linear copolymers of ethylene and alpha-olefin have an ESRD of less than 40%, less than 30% in another preferred embodiment, and from 10 to 40% in yet another preferred embodiment. In certain preferred embodiments, polymers suitable for the present invention may have an IISR of 1 to 40.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have an Mw of 10,000 to 500,000 g / mol, in another preferred embodiment of 10,000 to 250,000 g / mol. Preferably, Mw is from 20,000 to 200,000 g / mol, or from 25,000 to 150,000 g / mol in another embodiment.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers have a melting point T _p measured by differential scanning calorimetry ("DSC") of 90 or 95 or 100 ° C to 125 or 130 ° C. T _{p is} determined as follows: samples weighing from about 5 to 10 mg are sealed in aluminum sample cuvettes. DSC data is recorded, first, when the sample is cooled to -50 ° C, and then when gradually heated to 200 ° C at a speed of 10 ° C / min. The sample is kept at a temperature of 200 ° C for 5 minutes, after which a second cooling-heating cycle is carried out. Thermal effects are recorded during the first and second cycles. The melting temperature is measured and recorded during the second heating cycle (or second melting). Before measurement by DSC, the sample is aged (usually by holding it at room temperature for up to about 5 days) or annealing to increase the degree of crystallization.

In certain preferred embodiments, linear ethylene-alpha-olefin copolymers contain less than 5 ppm. hafnium, in another preferred embodiment, less than 2 ppm. hafnium, and less than 1.5 ppm hafnium in another preferred embodiment, and less than 1 ppm. hafnium in another preferred embodiment. In other preferred embodiments, linear ethylene-alpha-olefin copolymers contain from 0.01 to 2 ppm. hafnium, in another preferred embodiment, from 0.01 to 1.5 ppm. hafnium, and from 0.01 to 1 ppm hafnium or less, in another preferred embodiment, which is determined by inductively coupled plasma spectroscopy (ICP) as follows: a sample is introduced into the plasma in which it is atomized and the resulting atoms are ionized, while the electrons in the atoms are excited by switching to corresponding higher energy levels. When electrons return to their ground state (s), they emit radiation whose wavelength is a characteristic of each element. Elements present in the sample are determined by tracking the wavelength of the emitted radiation. The amount of each of the atoms present is determined based on the intensity of the waves of a given length when compared with the radiation intensities of known standard samples.

The molecular weight distribution (PMM) is M _w / M _n . Weighted average molecular weight (M _w ), number average molecular weight (M _n ) and z-average molecular weight (M _z ) are measured by gel permeation chromatography as described in 34 (19) Macromolecules 6812 (2001), which is fully incorporated into the present description as a reference. In such cases, a chromatograph for high temperature size exclusion chromatography (SEC, Waters Alliance 2000) is used, equipped with a differential refractive index detector (DIP) equipped with three columns of Polymer Laboratories PLgel 10 mm Mixed-B. The operation of the device is carried out at a flow rate of 1.0 cm / min and a sample volume of 300 μl. Various connecting lines, columns and a differential refractometer (DIP detector) are installed in the furnace, the temperature of which is maintained at around 145 ° C. Polymer solutions are prepared by heating a solution from 0.75 to 1.5 mg / ml of polymer in filtered 1,2,4-trichlorobenzene (TCB) containing about 1000 ppm. butylated hydroxytoluene (BHT) at 160 ° C for 2 hours with constant stirring. A sample of the polymer-containing solution is introduced into GPC and eluted using filtered TCB, including about 1000 ppm. OSH.

The separation efficiency of the column set is calibrated using several polystyrene standards with narrow PMMs corresponding to the expected range Mw of the analyzed sample and the exclusion limits of the column set. To create a calibration curve, 17 individual polystyrene standards are used, supplied by Polymer Laboratories (Amherst, Mass.), Whose peak molecular weight (MP) is from about 580 to 10,000,000. The flow rate is calibrated for each experiment in order to determine the position of the total peak of the flow rate marker (for which take a positive peak of sample injection), after which the retention volume of each of the polystyrene standards is determined. The peak position of the flow marker is used to correct the flow rate when analyzing samples. A calibration curve (the dependence of log (Mp) on the retention volume) is created by recording the retention volume at the peak value of the DIP signal for each polystyrene standard, and then this data set is approximated by second-order polynomial equations. Equivalent molecular weights of polyethylene are determined using the Mark-Hovink coefficients given in table 1.

Table 1 Odds Mark-Hovinka Material k (dl / g) BUT PS 1.75 × 10 ^-4 0.67 PE 5.79 × 10 ^-4 0.695

The composition distribution width index (ISRS) is defined as the mass content of copolymer molecules in which the monomer content is not more than 50% of the average total comonomer content. The ISRS of the copolymer is determined using well-known techniques for isolating the individual fractions of a copolymer sample calculated in accordance with WO 93/03093. One such technique for isolating individual fractions is elution fractionation with increasing temperature ("EFPT"), described in Wild, et al., 20 J. poly. Sci., Poly. phys. ed. 441 (1982) and US Pat. No. 5,008,204, which are incorporated herein by reference in their entirety. In such cases, a commercial analytical device for EFPT is used (Model 200, PolymerChar S.A.). A polymer sample is dissolved in a solvent, crystallized on a carrier and eluted from the carrier as the temperature of the mixture increases with an additional amount of the same solvent using a high-precision pump. The polymer chains are fractionated depending on the difference in crystallization and melting characteristics in the solvent. The concentration of the eluted polymer is monitored using an infrared detector. The polymer sample is dissolved in 1,2-dichlorobenzene (2 to 5 mg of sample per 1 milliliter of solvent at 160 ° C. for 60 minutes), and the resulting solution (0.5 ml) is introduced into the packing column for crystallization by the following steps : stabilization (temperature maintenance) at 140 ° С for 45 minutes, subsequent cooling to a temperature of 0 to 30 ° С at a rate of 1 ° C / min, stabilization (temperature maintenance) at a temperature of 0 to 30 ° С for 30 minutes. The sample was eluted from the column by pumping the solvent through the column at a flow rate of 1.0 ml / min for 10 minutes at 30 ° C. After that, the column temperature is increased to 140 ° C. by heating at a rate of 2 ° C./min, while maintaining a flow rate of the solvent passing through the column of 1.0 ml / min. The concentration of the eluted polymer is monitored using an infrared detector.

To separate the polymer into fractions of different chemical composition, a commercial device for preparative EFPT is used (Model MC2, Polymer Char S.A.). Approximately 2 g of the polymer is placed in a reactor, dissolved in 200 ml of xylene stabilized with BHT at a concentration of 600 ppm at 130 ° C. for about 60 minutes. The mixture was allowed to equilibrate for 45 minutes at 90 ° C, and then it was cooled to 30 ° C (standard procedure) or to 15 ° C (cryogenic method) at a cooling rate of 0.1 ° C / min. The temperature of the cooled mixture is increased until it reaches the planned range of the lowest temperature of selection (see table 2), and the mixture is heated to maintain its temperature in the specified range for 20 minutes. The mixture is subsequently filtered through a 75 μm filter column, and then through a 2 μm disk filter under a compressed nitrogen pressure of 10 to 50 psi. inch. The reactor is washed twice with 50 ml of xylene, heated to maintain the temperature of the washing mixture in a predetermined range, and maintained at this temperature for 20 minutes during each washing cycle. The fractionation process is continued by introducing fresh xylene (200 ml of xylene stabilized by BHT at a concentration of 600 ppm) into the reactor, increasing the temperature of the mixture until it reaches the next range of highest isolation temperatures, in accordance with the sequence indicated in table 2, and heating the mixture in order to maintain its temperature in the specified range for 20 minutes, after which filtering is performed as described above. The extraction cycle is sequentially repeated in this way until the mixture is extracted in all the temperature ranges of extraction indicated in Table 2. The extracted substances are independently precipitated with methanol in order to isolate individual polymer fractions.

table 2 The temperature ranges of the selection of fractions using a device for preparative EFPT chemical composition of the fraction, designations Compartment temperature Cryogenic technique Standard technique Range (° C) one - 0 to 15 2 one 15 to 36 * 3 2 36 to 51 four 3 51 to 59 5 four 59 to 65 6 5 65 to 71 7 6 71 to 77 8 7 77 to 83 9 8 83 to 87 10 9 87 to 91 eleven 10 More than 91 * The temperature range of selection for the standard method is from 0 to 36 ° C

Direct dynamic extraction is used to fractionate the polymer into fractions according to molecular weights as described in W. Holtrup, 178 makromol. chem. 2335 (1977). In such cases, a solution of 1 g of a polymer dissolved in 72 ml of hot (from 120 to 130 ° C) xylene, stabilized with 2 g of 2,6-di-tert-butyl-4-methylphenol per 4 liters of xylene for 1 , 5 hours in a device for preparative EFPT (Model MC2, Polymer Char SA), treated with 108 ml of precipitant (diethylene glycol monobutyl ether, MBDEG) for 30 minutes at a temperature of 120 ° C, and then filtered. The polymer is precipitated from the filtrate with an excess of methanol. The fractionation process is repeated by extracting the gel phase remaining in the reactor using xylene / MBDEG mixtures in the volume ratios described in Table 3. In all extraction experiments except the last, the indicated amount of xylene is added to the gel phase and the mixture is heated to a temperature from 120 to 130 ° C for 1 hour, after which MBDEG is added and the mixture is heated to a temperature of 120 ° C for 30 minutes, and then the mixture is filtered and the polymer fraction is precipitated with an excess of methane la. The last fractionation is carried out only using xylene.

Table 3 Volume ratios of xylene / MBDEG mixtures used for direct dynamic extraction Fraction Solvent Xylene MBDEG Volume ml Volume ml Percentage one 72.0 108,0 60.0 2 84.6 95.4 53.0 3 91.8 88.2 49.0 four 95.4 84.6 47.0 5 100.3 79.7 44.3 6 102.6 77.4 43.0 7 103.7 76.3 42,4 8 104.6 75,4 41.9 9 105.7 74.3 41.3 10 180 0 0

Spectroscopic analysis of ¹³ C NMR is carried out as follows: polymer samples for ¹³ C NMR spectroscopy are dissolved in d ₂ -1,1,2,2-tetrachloroethane at concentrations ranging from 10 to 15 wt%, after which they are introduced into the magnet of the spectrometer. ¹³ C NMR data was collected at 120 ° C. in a 10 mm sensor using a Varian spectrometer at a frequency of ¹ N of 700 MHz. During the entire data collection, a 90-degree pulse is used, the data collection duration configured to provide a digital resolution of 0.1 to 0.12 Hz, and a pulse delay of at least 10 pulses with constant broadband proton splitting using rectangular modulation of the scan pulse without transmission selection. The spectra are obtained using time averaging in order to ensure the ratio of signal intensities to noise, suitable for measuring the necessary signals. The assignment of ¹³ C NMR chemical shifts and the calculations used in the description of the polymers are carried out as described by M.R. Seger and G. Maciel in Quantitative With NMR Analysis of Sequence Distributions in Poly (ethylene-co-1-hexene), published in 76 anal. chem. 5734-5747 (2004). The concentration of triads is determined by integrating the spectra and normalizing to obtain a molar fraction of each of the triads: ethylene-ethylene-ethylene (EEE), ethylene-ethylene-hexene (EEG), ethylene-hexene-ethylene (EGE), hexene-ethylene-ethylene (GEE) ), hexene-ethylene-hexene (GEG), hexene-hexene-hexene (HHG). The observed concentrations of triads are converted to the concentrations of the following dyads: ethylene-ethylene (EE), hexene-hexene (GH) and ethylene-hexene (EG). After this concentration of dyads is used to calculate r ₁ r ₂ in accordance with the following formula:

$$r_{\mathrm{one}}{r}_2=\mathrm{four}*\frac{EE*GG}{{\left(EG\right)}^2}$$

The molar content of 1-hexene (% molar. Comonomer) is determined as follows:

% mol. hexene = (YYY + HGE + EGE) * 100

The pass number is determined as follows:

Pass number = (GEG + 1/2 * SEE) * 100

The average passage duration for ethylene is calculated by dividing the comonomer content by the passage number. Average passage time for ethylene = (GEG + EEG + EEE) / (passage number).

The content of butyl groups per 1000 carbon atoms is calculated by dividing the content of triads in the center of which 1-hexene is divided by the sum of the doubled content of triads in the center of which ethylene and the six-fold content of triads in the center of which 1-hexene are obtained the number is multiplied by 1000:

$$B\mathrm{at}t\mathrm{and}lbnsxR\mathrm{but}d\mathrm{and}\mathrm{to}\mathrm{but}l\mathrm{about}\mathrm{at}n\mathrm{but}1000\mathrm{but}t\mathrm{about}m\mathrm{about}\mathrm{at}\mathrm{at}gleR\mathrm{about}d\mathrm{but}=\frac{1000*\left(GGG+GGE+EGE\right)}{6*\left(GGG+GGE+EGE\right)+2\left(GEG+EEG+EEE\right)}$$

Proton ( ¹ H) NMR data was collected at 120 ° C. using a 5 mm sensor on a Varian spectrometer at a frequency of ¹ N at least 400 MHz. Data is recorded using a maximum pulse width of 45 degrees, the interval between pulses 8 s and 120 transitions to average the signal.

A linear copolymer of ethylene and alpha olefin can be prepared using any suitable polymerization process and catalyst. In a particularly preferred embodiment, a linear copolymer of ethylene and alpha-olefin is prepared by polymerizing ethylene and, optionally, alpha-olefin, using a catalyst comprising a hafnocene compound, the catalyst comprising from 95 to 99% mole. a hafnocene compound in one embodiment, and consists essentially of a hafnocene compound in another embodiment. In certain preferred embodiments, a hafnocene compound suitable for the polymerization of one or more olefins corresponds to the formula Cp ^A Cp ^B HfX _n in which each X is chemically bonded to Hf, each CP group is chemically bonded to Hf, an is 0, 1, 2, 3 or 4. Preferably, n is 1 or 2. Ligands corresponding to the formulas Cp ^A and Cp ^B may be the same or different cyclopentadienyl ligands or ligands, isobalic to cyclopentadienyl., one of them or both of them may contain heteroatoms, and one of them or they both can b be substituted with a group R in several positions. In a preferred embodiment, Cp ^A and Cp ^B are independently selected from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, and substituted derivatives of each of these compounds. Independently, each of Cp ^A and Cp ^B may be unsubstituted or substituted by any of R substituent groups or a combination of such groups. The catalyst compounds described herein are typically used with or without an activator (such as aluminoxane or a non-coordinating anionic activator (NAC)), together with a trialkyl aluminum acceptor or co-activator (such as triethyl aluminum, tri-n-octyl aluminum, triisobutyl aluminum). A catalytically active compound connected to an activator (and, optionally, a coactivator) is called a catalytic system.

In certain preferred embodiments of the method used to produce the linear ethylene-alpha-olefin copolymers described herein, the amount of monomer fed to the polymerization zone is adjusted to provide such a ratio of ethylene to alpha-olefin comonomer to produce polyethylene, the comonomer content of which (in volume) is from 0.5 to 25.0% mole. The reaction temperature, the residence time of the monomer in the reactor, the number of components of the catalyst system, and the nature of the molecular weight control agent (e.g., H ₂ ) can be varied to provide a linear copolymer of ethylene and alpha-olefin having the desired properties as described herein. Persons skilled in the art will be able to optimize such modifier relationships and predetermined conditions in the reactor in order to achieve the desired polymer melt index, density and / or other properties.

In certain preferred embodiments, at least one linear copolymer of ethylene and alpha-olefin is present in the outer layer (s) of the multilayer films described herein in an amount of 10 or 15 or 20 or 30 or 40 or 50 or 70 to 90 or 95 or 99% of the mass. based on the weight of the composition of which the layer consists. In a particular preferred embodiment, the outer layer (s) consists essentially of (up to 5% by weight of “additives” such as fillers, antioxidants, etc.) of at least one linear ethylene copolymer and alpha olefin.

The compositions used to produce the inner and outer layer (s) can be obtained by melt blown the desired polymer component and co-extruded the melts, or by mixing a linear copolymer of ethylene and alpha-olefin with one or more polymers such as LDPE, LDL, HDPE, etc. by combining the reactors in order to obtain reactor mixtures, or by using more than one catalyst in one reactor to produce several types of polymer. The polymers can be mixed with each other before they enter the film extruder or they can be mixed in an extruder that works in conjunction with a device for producing films.

The compositions can be molded using any conventional equipment and methods, for example, by dry mixing the individual components followed by mixing the melt in the mixer, or by mixing the components directly in the mixer, for example, a Banbury mixer, Haake mixer, Brabender internal mixer, or a single or twin screw extruder, which may include an extrusion mixer and a side extruder mounted directly downstream of the polymerization process, and it may include mixing powders or granules of polymers in the receiving container of the film extruder.

In addition, “additives” may be included in the outer and / or inner layers of the films and / or in the product obtained from the mixture, such as a film, if necessary. Such additives are well known in the art and may include, for example, the following components: fillers, antioxidants (e.g. spatially hindered phenolic compounds such as Irganox 1010 or Irganox ™ 1076 supplied by Ciba Corp.), phosphites (e.g. Irgafos 168, supplied by Ciba Corp.), adhesion inhibitors, tackifiers such as polybutenes, terpene resins, aliphatic and aromatic hydrocarbon resins, alkali metals, glycerol stearates and hydrogenated gums, UV stabilizers, thermally Kie stabilizers, antiblocking layers, release agents, antistatic agents, pigments, dyes, waxes, silica, talc and the like.

The components that make up each layer of the film can be mixed in the molten state using the same means used in the manufacture of films, or separately. In one of the preferred options, the components are combined using means for mixing the melts separately from similar means used in the manufacture of films. In a particular preferred embodiment, the components are combined in an extruder or high efficiency mixer, in one of the preferred embodiments, in a twin screw extruder. If necessary, shear forces and / or other heating means are applied to the components located in the extruder in order to increase the melt temperature, at least to the melting temperature of the refractory component itself, and at least to 160 or 180 or 200, or 220 or 230 C in particularly preferred embodiments. In certain preferred embodiments, the inner layer is extruded so that its melt has a higher temperature than the melt of the outer layer or layers, or vice versa. The temperature difference of the extrusion of the melts of the outer layers and the inner layer or layers is at least 15 or 20 or 25 or 30 or 40 ° C.

In order to obtain films from the compositions of the present invention, any method known in the art can be applied, for example, blown extrusion and casting, in addition, the compositions of the present invention can be used in an extrusion coating. In a particularly preferred embodiment, the compositions are used for the manufacture of blown films. You can use most of any equipment known in the art for producing blown films. In one aspect, upon receipt of the films of the present invention, there are some desirable extrusion conditions.

The speeds and performance of the extruder used to produce the films described herein are limited only by the characteristics of the equipment used. The speed of the extruder, its productivity and other process variables can be changed for each of the layers that are extruded to produce a film. The performance of the extruder (each individually or all of the extruders together) can be more than 50 or 80 or 100 or 150 or 200 kg / h in certain preferred embodiments, and can be from 50 or 80 or 100 or 150 to 400 or 500 or 600 or 800 or 1000 kg / h in other preferred embodiments. The melt temperature of the extrudate may be from 150 to 230 ° C in one of the preferred options, and from 160 to 200 ° C in a particular preferred embodiment. The melt pressure in the extruder (before or after a set of grids, if any) can be from 150 (15 MPa) to 500 bar (50 MPa) in one of the preferred options, and from 155 (15.5 MPa) to 400 bar ( 40 MPa) in another preferred embodiment. The set temperature of the extruder head may be from 150 to 280 ° C in one of the preferred embodiments, from 160 to 250 ° C in another preferred embodiment, and from 165 to 220 ° C in another preferred embodiment. Finally, the temperature of the head may be from 140 to 220 ° C in one of the preferred options and from 150 to 200 ° C in another preferred embodiment.

The films described herein have at least two, three or more layers, including at least one outer layer and at least one inner layer. As a rule, each of the layers is extruded separately, and then the layers are combined to form a film structure. In a particular preferred embodiment, three layers of the composition are extruded to form a three-layer film. In certain preferred embodiments, the final film forms a bursting bubble, wherein one layer, at least one outer layer and at least one inner layer are combined to form a new thick layer. Both the outer and inner layers of the final film preferably consist of a composition constituting the outer layer (s) of the bubble of the blown film. Preferably, the co-extrusion line of a blown film includes two, three or more (depending on the desired number of layers) extruders, melting, homogenizing and injecting the compositions to produce each of the film layers. Each of these extruders can have any set of desired sizes, regardless of the rest of the extruders. Additionally, any of the extruders may have a smooth feed zone or ribbed feed zone. In one embodiment, the extruder has a diameter of 30 or 40 mm to 50 or 60 or 80 or 90 or 100 or 200 mm and has a ribbed feed zone or feed channel with a smooth channel, preferably a feed zone with a smooth channel. In other preferred embodiments, the diameter of the extruder is from 40 to 80 mm, in another preferred embodiment, from 50 to 80 mm, and from 50 to 200 in another embodiment. Additionally, the extruders used in the film production process may have a length / diameter ratio of 20 to 50 in one embodiment, 25 to 45 in another embodiment, 15 to 60 in another embodiment, and 25 to 60 in another preferred embodiment.

The polymers and / or additional components of the compositions described herein can be fed into the extruder by any method known in the art, for example, using a gravimetric feed system in one of the preferred embodiments. Each extruder may be equipped with one, two, three, four, five or more feed containers, depending on the composition. Mixing in each extruder takes place in a special mixing container located below the feed containers, from which the mixture enters the extruder. Each extruder is connected to the head through a set of grids and an adapter. The flows of melts take shape in the head, passing through an annular hole.

After exiting the head, the tube-shaped melt is stretched and inflated in the form of a bubble using air supplied through the head in one of the preferred embodiments. Typically, cold air is introduced into the bubble, and warm air is extracted through the exhaust pipe. The diameter of the head may be from 100 to 500 mm in one of the preferred embodiments, from 190 to 350 mm in another preferred embodiment, from 200 to 300 mm in yet another preferred embodiment, and from 210 to 280 mm in yet another preferred embodiment. The degree of blowing (CP) of the films obtained by extrusion blown, can be from 1 to 10 in one of the preferred options, from 1.5 to 8 in another preferred embodiment, from 1.8 to 5 in another preferred embodiment, from 2.0 up to 3.5 in another preferred embodiment and from 2.2 to 3.0 in yet another preferred embodiment; the size of the hole in the head may be from 0.5 to 9 mm in one of the preferred embodiments, from 0.8 to 5 mm in another preferred embodiment, from 0.8 to 3 mm in another preferred embodiment and from 1.0 to 2, 0 mm in another preferred embodiment.

In any case, such air pressure leads to a rapid increase in the tube diameter by 3–9 times; this occurs at a height of about 5 to 10 head diameters above the head outlet from which the tube exits. An increase in the diameter of the tube is accompanied by a decrease in the thickness of its walls to a final value of about 12 to 50 μm, and the appearance of a biaxial orientation of the melt. The orientation of the film is characterized by the so-called "degree of shrinkage", which in the longitudinal direction is from 50 or 60 to 90 or 100, and in the transverse direction is from -40 or -30 to -10 or 0.

In certain preferred embodiments of the blown film process, the melt of the composition is simultaneously cooled externally using a double annular air gap. This annular gap provides the main cooling and provides a freezing line, the length of which can be from 100 or 500 to 1000 or 2000 mm in certain preferred embodiments. The cooling air can be cooled in a heat exchanger connected to a cold water supply circuit installed at the production site. In certain preferred embodiments, the bubble is stabilized in a calibration basket, the field of which the bubble goes to the stage of destruction. A flat tube exiting the framework to destroy the bubble immediately passes through a clamping roll, making the film flat. After that, the film can be directed through several spurious rolls to the device for centering the tape in order to align its position. From there, the film can be further sent to a corona treatment unit, and then sent to a winding machine.

Films obtained from the compositions of the present invention may have any number of layers and any thickness ratio. In a particularly preferred embodiment, a three-layer film is obtained having two outer layers and an inner layer located between the outer ones, with their ratio ranging from 1/1/1 to 1/20/1 in one of the preferred embodiments, from 1/2 1 to 1/15/1 in another preferred embodiment, and from 1/3/1 to 1/10/1 in another preferred embodiment. Each layer may have any desired thickness, which is from 1 to 100 μm in one of the preferred embodiments, from 2 to 80 μm in another preferred embodiment, from 2 to 60 μm in another preferred embodiment, from 3 to 40 μm in another one of the preferred options and from 4 to 15 microns in another of the preferred options. If we take into account all the variety of possible film structures, its total thickness can vary greatly. In one embodiment, the total film thickness or “film thickness” (including all layers) is from 10 to 500 microns, from 15 to 300 microns in another preferred embodiment, from 20 to 150 microns in another preferred embodiment, from 20 to 80 microns in another preferred embodiment, and from 20 to 50 microns, in yet another preferred embodiment. Naturally, the desired range of thicknesses of the layers and film may include any combination of any upper boundary and any lower boundary, as described in the present description.

Suitable processing stability is desirable, for example, at passage speeds exceeding 1.0 or 1.5 or 2.0 or 2.5 or 3.0 kg / h / cm of head circumference, and high linear speeds, for example, exceeding 50 or 60 or 70 or 80 m / min in the production of thin films on modern extrusion equipment. The films described herein can be processed at such high rates of productivity and speed. Persons skilled in the art will appreciate that varying travel speeds and linear speeds can be applied without departing from the spirit of the present invention (s).

In a particular preferred embodiment, the films described herein are obtained by co-extrusion of a composition forming the inner layer and at least one linear copolymer of ethylene and alpha-olefin through at least one die head to form a blown film, to obtain at least two compositions of the outer layers touching the inner layer on both sides, under the following conditions:

- a tensile speed of 2 s ^-1 or more (or 2 to 3 s ^-1 in another preferred embodiment) (the tensile speed (s ^-1 ) is (V _s -V ₀ ) / VLZ, where V _s represents the speed melt at the height of the freezing line, V ₀ represents the speed of the melt in the outlet of the head, and VLZ represents the height of the freezing line),

- the processing time (from the head to the freezing line) of 2 s or less (or from 0.5 to 2 s),

a blow ratio of 2.5 or less (or from 1.5 to 2.5 in another preferred embodiment),

- a freezing line height of 1.0 m or less (or 0.8 m or less, or 0.66 m or less, or 0.48 m or less, or from 1.0 to 0.1 m in other preferred options)

- head productivity of 2.0 kg / h / cm of head circumference or more (or 2.1 kg / h / cm of head circumference or more, or 2.5 kg / h / cm of head circumference or more in another preferred embodiment, or 2.9 kg / h / cm of head circumference in another preferred embodiment), and

- this process is carried out in such a way that three layers of ethylene polymer are formed, preferably a three-layer film with a thickness of 20 to 30 μm, the two outer layers comprising at least one linear copolymer of ethylene and alpha-olefin, I ₂₁ / I _{2 of} which is over 20.

In certain preferred embodiments, the inner layer of the films described herein includes at least one polyethylene, the total (connected polyethylene) density of which is at least. 0.910 g / cm or at least 0.920 g / cm ³ or at least 0.925 g / cm. In other preferred embodiments, differences in the (lowest) densities of the at least one outer layer or layers and the inner layer or layers (whose density is higher than the density of the outer layer or layers) will also generally result in higher transparency compared with two polyethylene with the same close density values. In certain preferred embodiments, the density difference should be at least 0.005 g / cm ³ or 0.010 g / cm ³ or 0.015 g / cm ³ or 0.020 g / cm ³ or 0.030 g / cm ³ or at least at least 0.040 g / cm ³ .

LDL suitable for use as components of the inner layer of films include linear low density polyethylene, the content of comonomer in which is from 0.5 to 20 wt. -%, and the comonomer is a derivative of C ₃ -C ₁₀ alpha olefins, preferably 1- butene or 1-hexene. The density of the desired LDL is from 0.910 to 0.940 g / cm ³ , in another preferred embodiment from 0.910 to 0.930 g / cm ³ , in another preferred embodiment from 0.912 to 0.925 g / cm ³ . The melt index (I ₂ ) of such LDL is from 0.1 or 0.2 or 0.4 to 4 or 6 or 10 dg / min. In one preferred embodiment, the LDL cholesterol used in the inner layer is cnLDP. In certain preferred embodiments, the inner layer comprises from 50 or 60 to 80 or 85 or 99% of the mass. LDL based on the mass of the inner layer.

PVPs suitable for use as components of the inner layer of films include linear low density polyethylenes, the comonomer content of which is from 0.01 to 5 wt%, the comonomer being a derivative of C ₃ -C ₁₀ alpha olefins, preferably 1- butene or 1-hexene, and is an ethylene homopolymer in certain preferred embodiments. The density of the desired PVP is from 0.945 to 0.970 g / cm ³ , in another preferred embodiment from 0.950 to 0.965 g / cm ³ , in another preferred embodiment from 0.955 to 0.965 g / cm ³ . The melt index (I ₂ ) of such PVP is from 0.1 or 0.2 or 0.4 to 4 or 6 or 10 dg / min. In one embodiment, the PVPs used in the inner layer are polymers prepared using Ziegler-Natta catalysts. In certain preferred embodiments, the inner layer comprises from 1 or 5 or 10 to 40 or 50% of the mass. PVP calculated on the mass of the inner layer.

High pressure polyethylene (LDPE), suitable for use as components of the outer and / or inner layers of the films, have a density of from 0.910 to 0.940 g / cm ³ , in another preferred embodiment, from 0.910 to 0.930 g / cm ³ , in a particular preferred a variant from 0.912 to 0.925 g / cm ³ . The melt index (I ₂ ) of such LDPE is from 0.1 or 0.2 or 0.4 to 4 or 6 or 10 dg / min, and is less than 1.0 dg / min in certain preferred embodiments. In certain preferred embodiments, the outer layer comprises from 0.1 or 1 or 2 to 8 or 10% of the mass. LDPE based on the mass of the outer layer. In certain preferred embodiments, the inner layer comprises from 0.1 or 1 or 2 to 8 or 10 or 20 or 30% of the mass. LDPE based on the mass of the inner layer. In other preferred embodiments, the LDPE is not substantially contained in the outer layers, in other preferred embodiments, the LDPE is not substantially contained in the inner layer, which means that the LDPE is not added to the composition of the layer or they are present in the composition in an amount of less than 5% of the mass. as an additional component of the masterbatch.

Certain preferred embodiments of the films described herein include: (I) an inner layer comprising from 50 or 60 to 75 or 95% of the mass. LDL calculated on the mass of the inner layer and from 5 or 25 to 40 or 50% of the mass. PVP calculated on the mass of the inner layer; and (II) two or more outer layers, including one or more linear copolymers of ethylene and alpha-olefin. Other specific preferred embodiments of the films described herein include: (I) an inner layer comprising from 55 or 65 to 85 or 95% of the mass. LDL calculated on the mass of the inner layer and from 5 or 15 to 34 or 45% of the mass. LDPE based on the mass of the inner layer; and (II) two or more outer layers, including one or more linear copolymers of ethylene and alpha-olefin. Other specific preferred embodiments of the films described herein include: (I) an inner layer comprising from 55 or 65 to 85 or 95% of the mass. LDL calculated on the mass of the inner layer and from 5 or 15 to 34 or 45% of the mass. one or more linear copolymers of ethylene and alpha-olefin based on the weight of the inner layer; and (II) two or more outer layers, including one or more linear copolymers of ethylene and alpha-olefin. Other preferred options for the films described in the present description include: (I) the inner layer comprising from 55 or 65 to 85 or 95% of the mass. LDL calculated on the mass of the inner layer and from 5 or 15 to 34 or 45% of the mass. linear copolymers of ethylene and alpha-olefin and PVP based on the weight of the inner layer; and (II) two or more outer layers, including one or more linear copolymers of ethylene and alpha-olefin. Other specific preferred embodiments of the films described herein include: (I) an inner layer comprising from 55 or 65 to 85 or 95% of the mass. LDL calculated on the mass of the inner layer and from 5 or 15 to 34 or 45% of the mass. one or more linear copolymers of ethylene and alpha-olefin based on the weight of the inner layer; and (II) two or more outer layers, including one or more linear copolymers of ethylene and alpha-olefin and PVD. The inner and / or outer layers may include from 0.1 to 3 or 4% of the mass. additives based on the weight of the layer, as described in the present description.

The thickness of the films described in the present description, in General, can be from 4 to 200 microns, to the greatest extent, it is determined by the intended method of application and the properties of the film. Stretch films can be thin; shrink films or bags designed for heavy loads have a significantly greater thickness. Suitably, the film thickness is from 5 to 200 microns, preferably from 10 to 180 microns, particularly preferably at least 25 microns. The thickness of each of the outer layers may be at least 7% of the total film thickness, preferably 10 to 40%. The thickness of the outer layer (s) may be less than the thickness of the inner layer. The thickness of the inner layer may be at least 20% of the total thickness. Nevertheless, in cases where this is more suitable, the outer layers may be thicker than the inner layers, for example, in cases where a large amount of linear polyethylene or a homogeneously branched linear polyethylene with a large number of branches, for example, metallocene polyethylene, is used in the inner layer Enable ™ (ExxonMobil Chemical Co.). The use of at least 10% of the mass. homogeneously branched linear polyethylene in the inner layer, with a layer distribution of 4/1/4, would limit the total amount of branched polyethylene to a value not exceeding 2% by mass, provided that the rest of the inner layer and the entire outer layer consist of unbranched polyethylene.

The films described herein, preferably a three-layer film of a thickness of 20 to 30 μm, in which two outer layers include at least one linear copolymer of ethylene and alpha-olefin, I ₂₁ / I ₂ which is more than 20, can be characterized by based on one or a combination of the following properties:

- impact strength, determined using a falling pointed load (ASTM D1709), component of more than 10 or 15 or 20 or 30 or 40 g / μm;

- turbidity (ASTM D1003, method B), component less than 10 or 8 or 5%;

- tensile strength in the longitudinal direction of more than 45 or 50 MPa;

- tensile strength in the transverse direction, comprising more than 35 or 40 MPa;

- 1% secant modulus in the longitudinal or transverse direction, comprising more than 290, or 300, or 310 MPa;

- tensile strength according to Elmendorf in the longitudinal direction, comprising more than 3 or 4 or 4.5 or 5 or 6 g / μm;

- tensile strength according to Elmendorf in the transverse direction, comprising more than 15 or 20 or 22 g / μm.

The films described herein can be adapted to produce flexible packaging films for a wide variety of applications, such as adhesive film, low-stretch film, inextensible film for wrappers, pallet film, multilayer film, agricultural film, sorting shrink film, and laminated films, including bags with a stable bottom. Films that can be used as bags are obtained in the form of bags, garbage bags and liners, industrial liners, bags for goods and bags of high strength. Bags can be obtained using vertical or horizontal equipment for molding, filling and corking. The film can be used in flexible packaging, food packaging, for example, freshly prepared products, packaging for frozen products, packaging, packaging and packaging of various products. The packaging including the film described above can be thermally sealed around the contents. Films and packaging may exhibit improved bond strength during molding and capping on capping equipment; improved optical properties, which are determined based on the measurement of turbidity, and improved stiffness and tensile resistance, which may be useful in some applications. Thin flexible films are easily compatible with other surfaces, and when used with suitable activation, they can be used as adhesive films. Thicker films containing a relatively higher amount of linear polyethylene can be stretched in the cold state and they exert a compressive force on the articles or stacks of products around which they are wrapped.

The tendency to shrink when heated can be used to obtain shrink films. By providing suitable outer layers, an inextensible film or extensible films can be sealed by heating. Transparent films can be used for packaging products and thermal sealing of bags. In this case, the films have the appropriate composition and structure and are obtained by such extrusion, which limits the ability to shrink when heated and the tendency to stretch. In the present description, such films are called packaging films. You can also get transparent films with the ability to shrink, which is usually achieved by introducing a polymer with branching of a long chain, which can be forced to shrink when heated. Such films are called shrink films. You can also get transparent films that can stretch at ambient temperature, in order to ensure the compressive action of the return force. Such films are called stretch films.

The present description provides examples of certain preferred options for multilayer films.

Examples

When applicable, the properties and descriptions of the films below cover measurements in the longitudinal and transverse directions. Such measurements are given separately, with "Pr" means a measurement in the longitudinal direction, and "PN" means a measurement in the transverse direction. Elmendorf tensile strength was measured in accordance with ASTM D1922. Tensile strength at yield strength was measured in accordance with ASTM D-882. Tensile strength was measured as described in ASTM D-882. Ultimate tensile strength was measured as described in ASTM D-882. Peak tensile load was measured as described in ASTM D-882. The energy of tensile rupture was measured as described in ASTM D-882. Elongation at yield strength was measured as described in ASTM D-882. Elongation at break was measured as described in ASTM D-882. A 1% secant modulus of elasticity was measured as described in ASTM D-882. Melt index 12 means melt flow rate measured in accordance with ASTM D-1238, condition E. High load melt index 1-c means melt flow rate measured in accordance with ASTM D-1238, condition F. Density was measured as described in ASTM D-1505 using flakes cut from injection molded plates in accordance with ASTM D-4703-07 aged for 40 hours at 23 ° C. plus / minus 2 ° C. unless specifically indicated otherwise. Impact strength, determined using a falling pointed load (also known as Dart F ₅₀ ), was measured in accordance with ASTM D-1709, Method A. Turbidity was determined in accordance with ASTM D1003, Method B using a Hunterlab color spectrophotometer.

Example 1. Blown films comprising outer layers consisting of linear ethylene-alpha-olefin copolymers

Received by extrusion blown and tested two films of the present invention and two comparative films. The characteristics of each film are shown in tables 4 and 5, the films have a layer distribution of 1/2/1. The linear copolymer of ethylene and alpha-olefin (EAO) used in these examples of the present invention had a melt index I _{2 of} 0.96 dg / min, a melt index I _{21 of} 21.7 dg / min, I ₂₁ / I _{2 of} 22.5 and a density (ASTM, flakes) of 0.9178 g / cm. The linear ethylene-alpha-olefin copolymers used in all examples were prepared using a supported catalyst derived from bis (n-propylcyclopentadienyl) hafnium dimethyl (Boulder Scientific, Colorado, USA) and Ineos ™ ES757 (microspherical silica with an average particle size of 25 μm ) with alumoxane (Al: Hf ratio of about 99: 1) in a 5000 ft ³ (about 142000 L) gas phase fluidized bed reactor operating at about 77 ° C. using an ethylene partial pressure of about 200 psi. inch (1.38 Pa), and when the ratio of hexane to ethylene equal to approximately 0.0150, when the content of isopentane is 10.0 mol%.

The following additives were included in the composition of the film of the present invention: 500 ppm Irganox 1076, 2000 ppm Weston ™ 399B (Phosphite, Borg-Warner Chemical Co.) and 800 ppm Dynamar ™ 5920A (fluoropolymer, 3M-Dyneon). Such a mixed EAO with additives had a melt index I _{2 of} 0.84 dg / min, a melt index I _{21 of} 20.3 dg / min, an I ₂₁ / I ₂ ratio of 24.2, and a density (ASTM, flakes ) of 0.9188 g / cm. Films A through D were three-layer films having two outer layers located on both sides of a single inner layer, the total thickness of the films ranged from 23 to 26 μm. Films A and C are films of the present invention, films B and D are comparative films.

The film structures are shown below, wherein LL1001 is an LDL obtained using Ziegler-Natta catalysts having 1z of 1.0 dg / min and a density of 0.918 g / cm (ExxonMobil Chemical Co.), HTA-108 is PVP, whose I ₂ is 0.70 dg / min, I ₂₁ is 46 dg / min, and the density is 0.961 g / cm (ExxonMobil Chemical Co.), and MB-42 is a mother liquor that prevents gel formation (10% wt. in PNP), Exceed ™ 1018 is an LDL obtained using a metallocene catalyst, I _{2 of} which is 1 , 0 dg / min, and the density is 0.918 g / cm (ExxonMobil Chemical Co.), and LD166 (I ₂ is 0.20 dg / min, density 0.923 g / cm) and LD150BW (I ₂ is 0.75 dg / min, density 0.923 g / cm ³ ) are low density polyethylene obtained under high pressure (LDPE) (ExxonMobil Chemical Co.):

Film A (of the present invention):

- inner layer: 68.4% of the mass. LL1001 + 30% of the mass. NTA-108 + 1.6% of the mass. MV42

- outer layers: 95% of the mass. EAO + 5% of the mass. LD150BW

Film B (comparative):

- inner layer: 68.4% of the mass. LL1001 + 30% of the mass. NTA-108 + 1.6% of the mass. MV42

- outer layers: 95% of the mass. Exceed 1018A + 5% wt. LD150BW

Film B (of the present invention):

- inner layer: 78.4% of the mass. LL1001 + 20% of the mass. LD166 + 1.6% of the mass. MV42

- outer layers: 100% of the mass. EAO Film G (comparative):

- inner layer: 78.4% of the mass. LL1001 + 20% of the mass. LD166 + 1.6% of the mass. MV42

- outer layers: 100% of the mass. Exceed 1018CA

The conditions for the production of blown films by Example 1 were as follows: a Windmoeller and Hoelscher blown film production line was used, the melt pressure was about 350 bar (35 MPa) before the mesh set, the degree of blowing was 2.5, the head diameter was 250 mm, and the thickness the gap in the head was 1.4 mm, the height of the freezing line was 840 mm, the speed of the exhaust roller was 74 m / min; temperature conditions were as follows: extruder A: 190 ° C, extruder B: 220 ° C, extruder B: 190 ° C, the temperature of the head housing was set at 220 ° C; The productivity of each extruder (for each layer) was: extruder A: 50 kg / h, extruder B: 100 kg / h, extruder B: 50 kg / h, the total productivity was 200 kg / h.

Example 2. Blowing films, including outer layers, consisting of linear copolymers of ethylene and alpha-olefin with a higher I ₂₁ / I ₂

Blown by extrusion and tested two films of the present invention and two comparative films, the films of the present invention containing outer layers comprising a linear copolymer of ethylene and alpha-olefin having a relatively higher I ₂₁ / I ₂ compared to example 1. Characteristics each film are shown in tables 6 and 7, the films have a layer distribution of 1/2/1. The composite (using the same additives as in Example 2) the linear copolymer of ethylene and alpha-olefin (EAO) used in these examples of the present invention had a melt index I _{2 of} 0.69 dg / min, melt index I ₂₁ , constituting 22.47 dg / min, I ₂₁ / I ₂ , constituting 32.6, and a density (ASTM, flakes) of 0.9213 g / cm. Films D through Z were three-layer films having two outer layers located on both sides of a single inner layer; the total thickness of the films ranged from 23 to 26 μm. Films D and G are the films of the present invention, films E and Z are comparative films.

The structures of the films are given below, with LL1001 being LDL obtained using Ziegler-Natta catalysts, NTA-108 is PVP, MV-42 is a mother liquor that prevents gel formation (10% wt. In PNP), Exceed ™ 1018 polyethylene represents LDL obtained using a metallocene catalyst (ExxonMobil Chemical Co.), and LD150BW and LD166 are low density polyethylene obtained under high pressure (LDPE) (ExxonMobil Chemical Co.), each of these components has the properties indicated in example 1:

Film D (of the present invention):

- inner layer: 78.4% of the mass. LL1001 + 20% of the mass. LD166 + 1.6% of the mass. MV42

- outer layers: 95% of the mass. EAO + 5% of the mass. LD150BW

Film E (of the present invention):

- inner layer: 78.4% of the mass. LL1001 + 20% of the mass. LD166 + 1.6% of the mass. MV42

- outer layers: 100% EAO Film F (comparative):

- inner layer: 78.4% of the mass. LL1001 + 20% of the mass. LD166 + 1.6% of the mass. MV42

- outer layers: 95% of the mass. Exceed 1018CA + 5% wt. LD150BW

Film Z (comparative):

- inner layer: 78.4% of the mass. LL1001 + 20% of the mass. LD166 + 1.6% of the mass. MV42

- outer layers: 100% of the mass. Exceed 1018CA

The conditions for obtaining films by extrusion blown in example 2 were the same as in example 1.

Table 4. Properties of the blown films of example 1 Property Film A Film B Film B Film G Impact strength A, determined using a falling pointed load The mass of the maintained load (g) 457.1 168.2 1186.7 240.0 The mass of the maintained load / microns (g / microns) 16.93 6.73 45.64 9.60 Longitudinal tensile strength properties Thickness (μm) 26 26 26 24 10% yield strength (MPa) 12.8 12.5 11,4 12.5 Manifested fluidity 2 (MPa) 14.0 13.9 15,2 16.7 Tensile Strength (MPa) 52,5 56.0 51.8 50,5 Elongation at break (%) 505 567 495 496 The energy of the gap (mJ / mm ³ ) 114 137 115 124 1% secant modulus of elasticity (MPa) 310 294 233 240 Strain Hardening Index (MPa) 21.0 18.5 20.3 18.2 The degree of stretching (%) 329 344 313 328 Maximum Holding Force (MPa) 15,5 fifteen 17.7 18.8 Transverse tensile strength properties Thickness (μm) 25 25 26 25 10% yield strength (MPa) 12.9 11.6 10.3 10.3 Manifested fluidity 2 (MPa) 11,4 10.7 10.0 10.1 Tensile Strength (MPa) 43,2 36.3 40.7 41.8 Elongation at break (%) 604 592 575 595 The energy of the gap (mJ / mm ³ ) 101 93 93 one hundred 1% secant modulus of elasticity (MPa) 333 289 283 278 Strain Hardening Index (MPa) 15.8 13,2 15.9 15.3 The degree of stretching (%) 414 410 387 390

Property Film A Film B Film B Film G Maximum Holding Force (MPa) 12.7 12.1 10.3 10.5 Elmendorf Tear Strength Elmendorf tensile strength (g / μm) in the longitudinal direction 6.36 6.97 4.13 4.25 Elmendorf tensile strength (g / μm) in the transverse direction 23.9 24.6 22.8 22.6 Puncture resistance Strength at break (N / μm) 2.88 3.02 3.32 3.76 Burst Energy (mJ / μm) 207 221 219 269 Table 5. Properties of the blown films of example 1 Property Film A Film B Film B Film G Turbidity (determined using the HUNTERLAB instrument) X 90.0 90.0 90.1 90.1 Y 91.8 91.8 91.9 91.9 Z 108.3 108,2 108.3 108.3 Turbidity 2.85 2.20 2.28 1.98 ZEHNTNER GLOSS, 45 ° gloss (°) (average of 5 measurements) 89.7 93,4 88.5 90.5 ZEBEDEE CL-100 device Transparency (%) (average of 5 measurements) 72.8 73,2 71.2 71.8 BETEX SHRINK device Longitudinal direction (%) +73 +76 +80 +81 Cross direction (%) -twenty -twenty -13 -13 Table 6. Properties of the blown films of example 2 Property Film D Film F Film E Film Z Impact strength A, determined using a falling pointed load The mass of the maintained load (g) 1163.3 364.3 673.3 240.8 The mass of the maintained load / microns (g / microns) 48.47 14.57 26.93 9.26 Longitudinal tensile strength properties

Property Film D Film F Film E Film Z Thickness (μm) 23 25 25 24 10% yield strength (MPa) 14.1 12,4 12.9 12,2 Manifested fluidity 2 (MPa) 18.2 15.9 17,2 16.3 Tensile Strength (MPa) 63.7 56.4 58.0 56.1 Elongation at break (%) 475 552 461 552 The energy of the gap (mJ / mm ³ ) 137 141 124 146 1% secant modulus of elasticity (MPa) 294 241 278 240 Strain Hardening Index (MPa) 25.7 19.0 22.7 18.5 The degree of stretching (%) 303 353 293 354 Maximum 20,2 18.0 19.3 19.0 Transverse tensile strength properties Thickness (μm) 24 25 25 25 10% yield strength (MPa) 12,4 10.9 11.6 10.9 Manifested fluidity 2 (MPa) 11.3 10.5 10.6 10.3 Tensile Strength (MPa) 39,4 43 37.9 45.9 Elongation at break (%) 590 589 595 620 The energy of the gap (mJ / mm ³ ) 97 one hundred 94 109 1% secant modulus of elasticity (MPa) 354 280 350 281 Strain Hardening Index (MPa) 15,2 16.9 15.1 16.1 The degree of stretching (%) 408 398 420 400 Maximum Holding Force (MPa) 11,4 10.0 10.8 10,2 Elmendorf Tear Strength Elmendorf tensile strength (g / μm) in the longitudinal direction 3.43 3.89 3.28 3,50 Elmendorf tensile strength (g / μm) in the transverse direction 21,2 25,2 24.7 23.7 Puncture resistance Strength at break (N / μm) 3.18 3.47 3.03 3.49

Property Film D Film F Film E Film Z Burst Energy (mJ / μm) 197 238 181 243 Table 7. Properties of the blown films of example 2 Property Film D Film F Film E Film Z Turbidity (determined using the HUNTERLAB instrument) X 89.8 89.9 90.0 89.9 Y 91.7 91.7 91.8 91.8 Z 107.7 107.9 108,0 108,0 Turbidity 4.01 2.18 3.88 1.26 ZEHNTNER GLOSS, 45 ° gloss (°) (average of 5 measurements) 78,4 91.4 78.8 94.5 ZEBEDEE CL-100 Transparency (%) (average of 5 measurements) 80 84 80 84 BETEX SHRINK device Longitudinal direction (%) +81 +79 +81 +81 Cross direction (%) -eleven -12 -12 -eleven

Further, after describing various properties and preferred embodiments of the film (s) of the present invention, numbered preferred embodiments of the present description are provided:

1. Blown film having an impact strength determined by a falling point load (ASTM D1709) greater than 10 g / μm and a haze (ASTM D1003, method B) of less than 10%, comprising at least , two outer layers and at least one inner layer located between the outer layers, the inner layer comprising at least one polyethylene, the total density of which is at least 0.910 g / cm ³ and the outer layers include at least one linear copolymer of ethylene and alpha olefin, the ratio of I ₂₁ / I ₂ which is more than 20, the density is from 0.910 to 0.945 g / cm, Mw / Mn is from 2.0 to 5.0, and at least 5% of the mass. soluble in xylene at 60 ° C or less, and the soluble part has the following properties:

- Mw (determined by gel permeation chromatography) is 150,000 g / mol or more;

- includes at least 5% mole. C ₃ -C ₂₀ comonomer as determined by ¹³ C NMR;

- the value of r ₁ r ₂ is 1.0 or less;

- the content of "butyl" groups per 1000 carbon atoms is 15 or more.

2. The film in accordance with the preferred option 1, in which at least one outer layer comprises from 0.1 to 20% of the mass. LDPE based on the mass of the outer layer.

3. The film in accordance with the preferred option 1 or 2, in which the inner layer comprises from 0.1 to 20% of the mass. LDPE based on the mass of the inner layer.

4. The film according to any one of the preceding preferred options, in which the inner layer essentially does not contain LDPE.

5. The film according to any one of the preceding preferred options, in which the inner layer includes at least one LDL.

6. The film according to any one of the preceding preferred options, in which the inner layer also includes PVP.

7. The film according to the preferred embodiment 6, the tensile strength in the longitudinal direction of which is more than 45 MPa, and its tensile strength in the transverse direction is more than 35 MPa.

8. The film according to any one of the preceding preferred options, in which the density of LDL is from 0.900 to 0.925 g / cm ³ .

9. The film according to any one of the preceding preferred options, in which at least one linear copolymer of ethylene and alpha-olefin has an I ₂₁ / I ₂ ratio of 20 to 35.

10. The film according to any one of the preceding preferred options, which has an impact strength determined using a falling pointed load (ASTM D1709) in excess of 15 g / μm.

11. The film according to any one of the preceding preferred options, in which at least the outer layer or layers have a lower density and the inner layer or layers have a higher density compared to the outer layer or layers, and the specified density difference is not less than 0.005 g / cm.

12. The film according to any one of the preceding preferred options, in which the IRIS of the linear copolymer of ethylene and alpha-olefin is less than 40%.

13. A film according to any one of the preceding preferred embodiments, in which a linear copolymer of ethylene and alpha-olefin is obtained by contacting at least ethylene, a hafnocene compound and an activator.

14. A method of producing a film according to any one of the preceding preferred options, comprising coextruding through a ring head of the melt composition of at least one inner layer having two front sides, and the composition of at least one outer layer, each of the outer layers located next to each side of the inner layer, followed by stretching the molten polymers in the form of a tube by extrusion with blowing of layered melts with the formation of a bubble using air supplied through the head.

15. The method according to the preferred embodiment 14, in which the extruder extrudes the melt of the inner layer and at least one extrudes the melt of the outer layers, and the combined productivity of the extruders is more than 50 kg / h

16. The method according to preferred options, number 14 or 15, in which the temperature difference of the extrudable melts of the outer layers and the inner layer or layers is at least 15 ° C.

17. The method according to preferred options 14 to 16, in which the films described in the present description, obtained by extruding a linear copolymer of ethylene and alpha-olefin through the head to obtain a film by blown extrusion at a stretching speed of 2 s ^-1 or more, duration a processing component of 2 s or less, a blowing degree of 2.5 or less, a freezing line height of 1.0 m or less, and a head capacity of 2.0 kg / h / cm of head circumference or more.

18. A blown film or method according to any one of the preceding preferred embodiments, comprising at least two outer layers and at least one inner layer located between the outer layers, said film having an impact strength determined by an incident pointed load (ASTM D1709) greater than 10 g / μm, turbidity (ASTM D1003, method B) less than 10%, tensile strength in the longitudinal direction of more than 45 MPa, and tensile strength in the transverse direction of more than 35 MPa

Claims (15)

1. The film for use in the manufacture of packages obtained by extrusion blown, comprising at least two outer layers and at least one inner layer located between the outer layers, in which:
A) the outer layers include at least one linear copolymer of ethylene and alpha-olefin, the melt flow rate (I ₂₁ / I ₂ ) of which is more than 20, a density in the range from 0.910 to 0.945 g / cm ³ , molecular weight distribution (Mw / Mn) ranges from 2.0 to 5.0, its composition distribution width index (ISRS) is less than 40%, and at least 5 wt.% Of the polymer is soluble in xylene at 60 ° C. or less, the soluble part having the following properties :
I) the weighted average molecular weight (Mw) (determined by gel permeation chromatography) is 150,000 g / mol or more;
II) includes at least 5 mol.% C ₃ -C ₂₀ comonomer, as determined by ¹³ C NMR;
III) the value of r ₁ r ₂ is 1.0 or less, calculated in accordance with the method in which ¹³ C NMR is used;
IV) the content of "butyl" groups per 1000 carbon atoms is 15 or more, and
B) the inner layer includes at least one polyethylene, the total density of which is at least 0.910 g / cm ³ ;
moreover, the film has an impact strength, determined using a falling pointed load (ASTM D1709), exceeding 15 g / μm, and a turbidity (ASTM D1003, method B) of less than 10%. 2. The film according to claim 1, in which at least one outer layer comprises from 0.1 to 20 wt.% High pressure polyethylene (LDPE) based on the weight of the outer layer. 3. The film according to claim 1, in which the inner layer includes from 0.1 to 20 wt.% LDPE based on the weight of the inner layer. 4. The film according to claim 1, in which the inner layer essentially does not contain LDPE. 5. The film according to claim 1, in which the inner layer includes at least one linear low density polyethylene (LDL). 6. The film according to claim 1, in which the inner layer also includes high density polyethylene PVP. 7. The film according to claim 6, the tensile strength in the longitudinal direction, which is more than 45 MPa, and its tensile strength in the transverse direction is more than 35 MPa. 8. The film according to claim 1, in which the density of LDL is from 0.900 to 0.925 g / cm ³ . 9. The film according to claim 1, in which at least one linear copolymer of ethylene and alpha-olefin has an I ₂₁ / I ₂ ratio of 20 to 35. 10. The film according to claim 1, in which at least the outer layer or layers have a lower density, and the inner layer or layers have a higher density compared to the outer layer or layers, and the specified density difference is at least 0.005 g / cm ³ . 11. The film according to claim 1, in which a linear copolymer of ethylene and alpha-olefin is obtained by contacting at least ethylene, a hafnocene compound and an activator. 12. The method for producing a film according to claim 1, comprising coextruding through the annular melt head a composition of at least one inner layer having two faces and a composition of at least one outer layer, each of the outer layers being adjacent on each side of the inner layer, followed by extrusion of the molten polymers in the form of a tube by extrusion with blowing of layered melts with the formation of a bubble using air supplied through the head. 13. The method according to item 12, in which the extruder extrudes the melt of the inner layer and at least one extruder extrudes the melt of the outer layers, and the combined productivity of the extruders is more than 50 kg / h 14. The method according to item 12, in which the temperature difference of the extrudable melts of the outer layers and the inner layer or layers is at least 15 ° C. 15. The method according to item 12, in which the films described in the present description, obtained by extruding a linear copolymer of ethylene and alpha-olefin through the head to obtain a film by extrusion blown under the following conditions:
I) the stretching speed is 2 s ^-1 or more,
Ii) the processing time is 2 s or less,
Iii) the degree of inflation is 2.5 or less,
Iv) the height of the freezing line is 1.0 m or less, and
V) head capacity is 2.0 kg / h / cm of head circumference or more.